Accepting an offer means to build on it in some way, as a real part of the scene - in the way you mean.
A block is when you ignore or undermine the offer, denying it instead of building on it. There's temptation to do so for a cheap laugh. The uncharitable negativity of HN seems similar.
For example, if someone starts a scene with "Isn't it lovely to be here in Paris?", I accept that we are in Paris, but I don't have to think it's lovely.
The takeaway from this to non-improv discussions is that I'm more aware of the fact that although I might disagree with the comment someone makes, I accept that the writer has that opinion and that they believe it to be true, and if I want to challenge any part of it then I'm going to have a much better time of it if I start from their version of reality.
Why? They perfectly highlight what's the "good common-sense reply" is like, how we should measure with each other opinions and how to handle disagreements.
HN might as well included the conversation as an example.
The steelmanning combinatorially #buildingmentalhealth and emotional regulation while mods are drone operators hiddren unrestricted violently cutting and copping audit logs to get page views clear for what depth of order of self empowerment determination?
[1] http://web.archive.org/*/https://news.ycombinator.com/item?i... [2] https://archive.today/https://news.ycombinator.com/item?id=9... [3] http://www.webcitation.org/query?id=1428133249694151